The present invention generally relates to implantable cardiac pacemakers. More specifically, the present invention relates to the sensing parameters of biatrial and/or biventricular pacing systems.
Modern implantable pacemakers are provided in various configurations to provide particular therapies. Certain variations of these pacemakers sense and/or pace within two, three or four chambers of the heart. Early pacemakers generally included a single atrial lead and/or a single ventricular lead, thus limiting both sensing and pacing functions. More recently, pacemakers have been utilized having biatrial and/or biventricular lead configurations. Thus, pacing and sensing can be targeted to more specific areas within the heart.
One type of cardiac event handled by implantable pacemakers is the premature ventricular contraction (PVC). A PVC can generally be identified by a pacing system as a ventricular sensed event that follows another ventricular event without an intervening atrial event.
Once a PVC has been identified, various pacing systems will react to the event. One type of PVC response is the initiation of an extended post-ventricular atrial refractory period (PVARP) of 400 ms. An extended PVARP is a predetermined time window, during which atrial events are ignored or xe2x80x9cblankedxe2x80x9d out. This is a preventative mechanism to avoid detecting retrograde P waves within the atrial chambers and inadvertently triggering a pacemaker mediated tachycardia (PMT).
The use of an extended PVARP within the programming of an implantable pacemaker is an effective safety mechanism to avoid PMT. However, with the advent of biventricular pacing and sensing, a new problem arises in that the dual sensing of the same ventricular event will retrigger the initiation of the extended PVARP. Thus, instead of having a window of 400 ms, the extended PVARP is effectively extended by the length of the interventricular conduction delay (IVCD), which is usually between 80-180 ms. This makes the xe2x80x9ctotalxe2x80x9d extended PVARP too long in that intrinsic conduction will occur within the heart and be misclassified as a PVC. This will become a repetitive cycle known as extended ventricular sensing.
To avoid this condition, implantable pacemakers having biventricular sensing capabilities have been programmed so as to disable the extended PVARP function. This does effectively avoid the initiation of extended ventricular sensing. It also means that a useful safety feature, namely the PVC response function, is bypassed and unused. This is undesirable in that pacemaker mediated tachycardia becomes possible.
Table 1 lists patents that disclose pacemakers that provide biatrial and biventricular pacing. Typically, these references fail to address the issues arising from the use of an extended PVARP within a multi-site pacing system.
All patents listed in Table 1 above are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Preferred Embodiments and claims set forth below, many of the devices and methods disclosed in the patents of Table 1 may be modified advantageously by using the techniques of the present invention.
The present invention has certain objects. That is, various embodiments of the present invention provide solutions to one or more problems existing in the prior art with respect to cardiac pacing in general, and facilitate the use of the PVC response feature in biventricular sensing configurations, in particular. Such problems include, for example, having to disable the PVC response function in biventricular pacing systems. Specifically, previous biventricular pacing systems have had to be programmed so as to disable the initiation of an extended PVARP that would otherwise occur in response to a detected PVC. Other problems include the possibility of allowing pacemaker mediated tachycardia to occur in biventricular pacing systems having the PVC response function disabled in order to avoid extended ventricular sensing.
Various embodiments of the present invention have the object of solving at least one of the foregoing problems. While some biventricular pacing systems have been able to prevent extended ventricular sensing, they have required that the PVC response function be disabled. Thus, these prior biventricular pacing systems have only been able to deal with one problem or the other, and not both. Thus, one condition always remains as a possibility. It is therefore another object of the present invention to provide an improved apparatus and methodology for allowing a biventricular pacing system to appropriately respond to detected PVC""s with the appropriate PVC response while also preventing extended ventricular sensing from occurring in a problematic context.
In comparison to known implementations of cardiac pacing systems and methodologies, various embodiments of the present invention may provide one or more of the following advantages: allowing the use of the PVC response feature on biventricular and biatrio pacing system and preventing extended ventricular sensing from occurring while the PVC response feature is enabled.
Some embodiments of the invention include one or more of the following features: a mechanism that works in conjunction with the extended PVARP function so that both extended ventricular sensing and pacemaker mediated tachycardia are prevented. For example, the present invention triggers a programmable ventricular blanking period in conjunction with the extended PVARP to accomplish this object.
Another feature of the present invention is a pacing system that accommodates the dual sensing of the same ventricular event by a biventricular pacing system. For example, the present invention provides a programmable ventricular blanking period to generally coincide with a measured inter-ventricular conduction delay so as to account for this dual sensing.
Yet another feature of the present invention is a pacing system having an algorithm that allows a PVC response to properly function in the context of a biatrio-biventricular pacing system. (Bi)atrio-biventricular is meant to include a biventricular system that may include a biatrial component or may only pace/sense a single atrial chamber.
In a biventricular system, a first ventricular lead is placed in the right ventricle and a second ventricular lead is placed in the left ventricle. Thus, each ventricular event will typically be sensed twice by the pacing system as the cardiac depolarization wave moves around the heart. More specifically, one of the ventricular leads will first sense the event (designated R1) and at some time interval later (generally  greater than 100 ms), the other ventricular lead will then separately sense the same event (designated R2).
In the context of a PVC response, each repetitive sense of the ventricular event will restart the extended PVARP. As such, the predetermined time period of the extended PVARP is effectively increased by an amount of time equal to the inter-ventricular conduction delay (IVCD). The IVCD is essentially the time delay between R1 and R2. Naturally occurring P waves will not be sensed during this extended time period and consequently, any intrinsic AV conduction will allow spontaneous R waves to occur which will be falsely classified as a PVC. This leads to a repetitive cycling where therapy to the patient is lost until the atrial rate slows down.
Thus, another feature of the present invention may be a programmable ventricular blanking period (VBP) that is initiated when the extended PVARP is initiated. The programmable VBP exceeds the IVCD so that repetitive sensing of the same ventricular event will not restart the extended PVARP. Because the extended PVARP is not reset, it functions as intended and the repetitive cycling described above is avoided. In this manner, therapy is consistently delivered to the patient without interruption due to extended ventricular sensing.
The above summary of the present invention is not intended to describe each embodiment or every embodiment of the present invention or each and every feature of the invention. Advantages and attainments, together with a more complete understanding of the invention, will become apparent and appreciated by referring to the following detailed description and claims taken in conjunction with the accompanying drawings.